Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
  • C01C3/00—Cyanogen; Compounds thereof
  • C01C3/004—Halogenides of cyanogen

Definitions

• the present invention relates to a continuous process for preparing chlorocyan, which is, in particular, suitable for the industrial scale.
• Chlorocyan is used in large quantities, particularly for preparing cyanuric chloride but also for preparing many other chemical products.
• chlorocyan is prepared from hydrocyanic acid and chlorine (Ullmann, Encyclopedia of Industrial Chemistry, Vol. 8, 1987, p. 197, VCH).
• the chlorocyan is advantageously processed further immediately to form the desired trimerization product. Because of the hazards involved in the transport of hydrocyanic acid over large distances, the chlorocyan plants should be located directly next to a hydrocyanic acid production site.
• sodium cyanide is simultaneously reacted in aqueous solution with chlorine.
• the choice of sodium cyanide as raw material results in only sodium chloride being obtained as by-product in the reaction rather than, as when hydrogen cyanide is used, hydrochloric acid which strongly accelerates the hydrolysis of hydrogen cyanide to formic acid and ammonium chloride.
• Sodium cyanide is preferably used in the form of a 10-40% strength aqueous solution, more preferably a 15-35% strength aqueous solution and particularly preferably as an aqueous solution having the customary commercial concentration of about 30%.
• Water can preferably be additionally introduced into the reaction. The addition of water is set as a function of the concentration of the sodium cyanide solution so that the sodium chloride concentration in the wastewater is in the range from 10 to 20%.
• the chlorine can be used as liquid chlorine or in gaseous form.
• Chlorine is preferably used as (technical-grade) gas in the process of the invention, which is of importance both for the economics and for plant safety.
• the amount stored in a plant can be kept extremely small even in the case of industrial-scale production and hazards to personnel and the environment due to the storage of chlorine water can be virtually ruled out.
• the metered addition of sodium cyanide and chlorine is preferably regulated by means of a quantity measurement as a function of the prescribed concentration of the raw materials.
• the ratio of the reactants is preferably set via a ratio regulation so that, per mole of sodium cyanide, from 1.00 to 1 .10 mol, more preferably from 1.03 to 1 .06 mol, in any case a small excess, of chlorine are/is used.
• the molar ratio of the reactants is therefore set by pH regulation, so that a pH of from 1.0 to 7.0, preferably from 2.0 to 4.0, particularly preferably about 3, is maintained in the reaction solution. At this pH, the reactants react immediately in the desired way. If the pH is too low, there is a risk of nitrogen trichloride formation and undesirable hydrolysis of sodium cyanide, while if the pH is too high, there is a risk of cyanide polymerization, leading to strongly discoloured wastewater.
• the raw materials are simultaneously metered separately into a reactor with good mixing and the sodium chloride water formed is removed continuously.
• the reaction solution formed can be taken off continuously.
• chlorocyan and chlorine can be driven off from the reaction solution discharged and be recirculated to the reactor before the solution is passed to wastewater treatment.
• a reactor e.g. residence reactor
• a reactor e.g. residence reactor
• Suitable reactors are, for example, circulation reactors with static mixers or mixing nozzles or stirred reactors having a sparging stirrer.
• the chlorine content of the gaseous chlorocyan formed can be set to any value in the range from 0% to 10% as a function of the reaction temperature together with the liquid level in the reactor and the molar ratio of sodium cyanide to chlorine.
• a significant advantage of the process of the invention is that the reaction can, in contrast to the processes of the prior art, also be carried out at elevated temperature, in particular from 30°C to 80°C, preferably from 40 0 C to 60°C, without increased secondary reactions occurring.
• elevated temperature in particular from 30°C to 80°C, preferably from 40 0 C to 60°C.
• This has important consequences from an ecological and processing engineering point of view.
• the tremendous amount of heat evolved in the reaction can be utilized, firstly, to heat the reactants which are metered in cold, and secondly the excess heat can be removed easily by means of a heat exchanger operated using cold water.
• the temperature gradient from reaction solution to cooling water is not sufficient for economical operation, so that electric cooling energy, e.g. cooling brine, has to be employed.
• the process of the invention makes it possible to prepare chlorocyan in a very environmentally friendly way in very good yields and very high purities of up to 99% from industrially available raw materials, which is why this process is particularly suitable for the industrial scale.
• the utilization of capacity can be varied in a very wide range by means of the type of reactor selected, which significantly increases the flexibility on an industrial scale.
• the following examples illustrate the invention.
• the circulation reactor CR 200 provided with temperature, level and pH measurement, circulation pump and heat exchanger CT 205 was operated continuously.
• the metering system comprised two inlet tubes for gaseous chlorine and aqueous sodium cyanide solution located opposite one another at the bottom of the reactor.
• the average circulating flow was 32 m 3 /h.
• the circulation reactor CR 200 was superposed by the scrubber CA 200 which was supplied with water in order to set the desired sodium chloride concentration in the reactor and at the same time be able to scrub out any free hydrogen cyanide from the gaseous chlorocyan.
• the desired reaction temperature was set by means of the heat exchanger CT 205.
• the chlorocyan formed was cooled to about 30°C by means of the heat exchanger CT 204 in order to reduce the water content correspondingly to the partial pressure.
• the desired level in the reactor was set by means of the regulating valve LIC 1281 and the excess reaction solution (mainly sodium chloride together with a little dissolved chlorocyan and chlorine) was fed continuously to the stripper (vacuum evaporator) CA 201 .
• the temperature was kept at the boiling point by means of the heat exchanger CT 201 and dissolved chlorocyan and chlorine were recirculated via the heat exchanger CT 200 to the circulation reactor CR 200.
• the sodium chloride solution was passed via a free overflow to wastewater treatment.
• the reactor CR 200 (level: 2.40 m) and the stripper CA 201 were initially filled with water to overflowing via the scrubber CA 200.
• the heat exchanger CT 201 was then supplied with steam and the other heat exchangers were supplied with cooling water.
• the introduction of water was set to 800 kg/h and metered introduction of chlorine (350 kg/h) was commenced.
• 30% strength sodium cyanide solution having a sodium hydroxide content of 1.4% was added and the pH was observed.
• the chlorine/sodium cyanide ratio was altered until the pH was in the range from 2.0 to 4.0.
• the heat exchanger CT 205 was supplied with cooling water so that a reaction temperature of from 45°C to 50°C could be maintained.
• the reactor CR 200 (level: 3.20 m) and the stripper CA 201 were initially filled with water to overflowing via the scrubber CA 200.
• the heat exchanger CT 201 was then supplied with steam and the other heat exchangers were supplied with cooling water.
• the introduction of water was set to 800 kg/h and metered introduction of chlorine (350 kg/h) was commenced.
• 30% strength sodium cyanide solution having a sodium hydroxide content of 1 .4% (about 800 kg/h) was added and the pH was observed.
• the chlorine/sodium cyanide ratio was altered until the pH was in the range from 2.0 to 4.0.
• the heat exchanger CT 205 was supplied with cooling water so that a reaction temperature of from 45°C to 50°C could be maintained.
• Raw material Amount NaCN/CI2 Fill height Chlorocyan Yield CI2 in the CICN
• the reactor CR 200 (level: 1 .60 m) and the stripper CA 201 were initially filled with water to overflowing via the scrubber CA 200.
• the heat exchanger CT 201 was then supplied with steam and the other heat exchangers were supplied with cooling water.
• the introduction of water was set to 800 kg/h and metered introduction of chlorine (350 kg/h) was commenced.
• 30% strength sodium cyanide solution having a sodium hydroxide content of 1 .4% (about 800 kg/h) was added and the pH was observed.
• the chlorine/sodium cyanide ratio was altered until the pH was in the range from 2.0 to 4.0.
• the heat exchanger CT 205 was supplied with cooling water so that a reaction temperature of from 45°C to 50°C could be maintained.
• the reactor CR 200 (level: 3.20 m) and the stripper CA 201 were initially filled with water to overflowing via the scrubber CA 200.
• the heat exchanger CT 201 was then supplied with steam and the other heat exchangers were supplied with cooling water.
• the introduction of water was set to 800 kg/h and metered introduction of chlorine (350 kg/h) was commenced.
• 30% strength sodium cyanide solution having a sodium hydroxide content of 1 .4% (about 800 kg/h) was added and the pH was observed.
• the chlorine/sodium cyanide ratio was altered until the pH was in the range from 2.0 to 4.0.
• the heat exchanger CT 205 was supplied with cooling water so that a reaction temperature of from 65°C to 70°C could be maintained.
• the reactor CR 200 (level: 2.40 m) and the stripper CA 201 were initially filled with water to overflowing via the scrubber CA 200.
• the heat exchanger CT 201 was then supplied with steam and the other heat exchangers were supplied with cooling water.
• the introduction of water was set to 800 kg/h and metered introduction of chlorine (350 kg/h) was commenced.
• 30% strength sodium cyanide solution having a sodium hydroxide content of 1 .4% (about 800 kg/h) was added and the pH was observed.
• the chlorine/sodium cyanide ratio was altered until the pH was in the range from 2.0 to 4.0.
• the heat exchanger CT 205 was supplied with cooling water so that a reaction temperature of from 30°C to 35°C could be maintained.

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Treatment Of Water By Oxidation Or Reduction (AREA)
• Removal Of Specific Substances (AREA)

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• 2007
  • 2007-11-01 DE DE200710052538 patent/DE102007052538A1/de not_active Withdrawn
  • 2007-11-23 CN CNA2007101936589A patent/CN101423230A/zh active Pending
• 2008
  • 2008-10-23 WO PCT/EP2008/064367 patent/WO2009056483A2/en active Application Filing

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